Cryosurgical instruments in which the probe tip is cooled with assistance of the Joule-Thomson effect provided by flow-through of a gas such as laughing gas (N.sub.2 O) or carbon dioxide (CO.sub.2), have in the last few decades found application for surgical purposes with good results (Archives of Pathology, May 1948, Pages 565 and 566). This holds also for other known cryosurgery instruments, in which the probe tip is cooled by vaporization of a liquefied gas.
In the case of cryosurgical instruments of these two kinds, it is further known and common to provide an electrical heating device in the region of the probe tip, that is intended to make possible a quick thawing of the probe (German OS NO. 24 22 103), and which is intended to serve also for temperature control with respect to the cryosurgical instruments utilizing the Joule-Thomson effect, because it is not sufficient in certain cases by adjustment, for example, of the outlet valve of the gas flask to control the supplied gas quantity in such a way that a suitable temperature of the probe tip can be obtained (German Pat. No. 15 41 099). By these electrical heating devices, the cooling effect obtainable by the Joule-Thomson effect can be raised or compensated more or less for the purpose of temperature control, or a warming-up can take place again after issue from the constricted gap in order to establish a suitable temperature in this manner.
Such cryosurgical instruments in which the supply duct is provided inside the discharge duct in the probe, and where an outlet nozzle is arranged at the end of the supply duct, have proved themselves in practice to be satisfactory. On the other hand, it would nevertheless be more useful to design the inner of the two coaxially arranged ducts as the discharge duct, so that the cold gas would be guided back through the inner duct, so that no additional cooling down of the probe shaft would be produced by the cold gas. In a known proposal of this kind (German Pat. No. 15 41 099), the inner discharge duct has at its end an outer flange which has such an outer diameter that between the circumference of the flange and the inner surface of the probe there is present a very small spacing or a series of spacings which are formed by irregularities of the flange and constitute a constriction. The heating winding necessary for control of the temperature can in such case be arranged adjacent to the flange of the discharge duct. Apart from the disadvantage that such devices require a current supply on account of the heating winding, it is not possible without some further provision to obtain a suitable control of the temperature because the thermal expansion or contraction of the elements which bound the gap cannot directly be controlled through current supply to the heating winding in such a way that a suitable gap size can be maintained.